Internal combustion engines with pre-chambers are known from the state of the art. In internal combustion engines, as from a given displacement volume, the energy of an ignition spark of a spark plug alone is no longer sufficient to reliably ignite the fuel gas-air mixture which is frequently very lean for emission reasons in the main combustion chamber. Pre-chamber engines therefore have a further combustion chamber which is only a fraction of the volume of the main combustion chamber and in which a fuel gas-air mixture is ignited by an ignition device. That pre-chamber communicates with the main combustion chamber by way of a passage. The ignition flares flash over into the main combustion chamber through the transfer flow bores at the end of the passage, that is at the main combustion chamber, and ignite the mixture which is present in the main combustion chamber.
In a so-called unflushed pre-chamber, during the compression cycle, mixture is urged out of the main combustion chamber into the pre-chamber, and therefore the same gas-air mixture is present in the main combustion chamber and the pre-chamber. If in contrast the pre-chamber is additionally supplied with fuel gas or mixture then reference is made in that case to a flushed pre-chamber. In the case of flushed pre-chambers therefore in order to increase the ignition energy of the pre-chamber the mixture in the pre-chamber is enriched with a small amount of fuel gas or an additional fuel.
EP 0377265 describes for example a gas engine having a pre-chamber which is supplied with fuel gas through a gas conduit 18. A non-return valve 24 opens when the required opening differential pressure is achieved and permits fuel gas to pass to the pre-chamber.
An internal combustion engine of the general kind set forth here has a pre-chamber which can be supplied with fuel gas by a pre-chamber gas supply section. Metering of fuel gas from the pre-chamber gas supply section into the pre-chamber is effected by a pre-chamber gas valve. The pre-chamber gas supply section itself is fed with gas from the gas supply of the internal combustion engine. For setting the desired pre-chamber gas amount the gas feed is generally effected by way of central aperture between the main gas supply and the pre-chamber gas supply section.
The pre-chamber gas valve is generally in the form of a passive non-return valve which opens only at a given positive difference between the pressure of the gas supply and the pressure in the pre-chamber, and thus meters out a given amount of gas to the pre-chamber. If the pressure is below the opening differential pressure the pre-chamber gas valve remains closed.
As the pre-chamber gas supply is frequently coupled to the compressor of the internal combustion engine the pressure in the pre-chamber gas supply generally corresponds to the charge pressure or is linked thereto.
If the compression curve of the main combustion chamber is considered then opening of the pre-chamber gas valve takes place during the charge change, when the opening differential pressure of the pre-chamber gas valve is exceeded.
Due to the abrupt opening of the pre-chamber gas valves when a sufficiently great pressure difference is achieved between the pressure in the pre-chamber gas supply conduit and the main combustion chamber, pressure fluctuations are imposed on the gas volume in the pre-chamber gas conduit. Those pressure fluctuations can influence the desired opening times of the pre-chamber gas valves as well as the supplied amount of gas, including for other cylinders.
More specifically, the pressure fluctuations in the pre-chamber gas supply conduit provide that a different pressure from the nominal pressure of the pre-chamber gas supply occurs locally before a pre-chamber gas valve and therefore that pressure ratio between the pre-chamber gas supply conduit and the main combustion chamber, that causes opening of the pre-chamber gas valve, is attained for an excessively short time, too long or not at all.
The consequence is that an undefined amount of fuel gas is fed to the pre-chambers, this being at indefinite times.
Deviations from the predetermined amount of fuel gas fed to the pre-chamber have negative influences on the emissions, the efficiency and the combustion stability of the internal combustion engine. For example, with an excessively low feed of fuel into the pre-chamber there is the risk that the pre-chamber cannot reliably ignite the main combustion chamber.
In order therefore to moderate the pressure fluctuations which are imposed on the column of gas in the pre-chamber gas supply there are usually provided in that conduit portion communicating the pre-chamber gas supply conduit with the individual pre-chamber gas valves, apertures (therefore additional “decentral” apertures in relation to the “central” aperture between the main gas supply and the pre-chamber gas section), through which the gas can only flow in throttled relationship.
Those local apertures which are known per se from the state of the art provide that the volume between the aperture and the pre-chamber gas valve fills in a slowed-down process. Fluctuations in the pre-chamber gas supply conduit (“rail”) are reduced due to that slow “charging”. This also provides that the abrupt opening of the pre-chamber gas valve cannot transmit pressure fluctuations to the pre-chamber gas supply, or can transmit only heavily damped pressure fluctuations. That is intended to provide that the same amount of fuel gas is always fed to all pre-chambers which are respectively associated with a combustion chamber of the internal combustion engine.
It is known however that deviations in the variation in cylinder pressure during the charge change and the high-pressure phase occur between the cylinders of an internal combustion engine including a plurality of combustion chambers. That so-called cylinder inequality is already inevitable for the reason that there are geometrical deviations between the piston-cylinder units and flow effects in the charge change. A disadvantage in that respect is that a low pressure in the pre-chamber during the charge change leads to a greater amount of pre-chamber gas supplied, and vice-versa.
Differences in the pre-chamber gas valves and in the cylinder-individual parts of the pre-chamber gas supply also lead to further contributions to cylinder inequality.